Fuel regulating apparatus for aircraft gas turbine power plants



Dec. M. A. EDWARDS ET A1. 2,622,393

FUEL REGULATING APPARATUS FOR AIRCRAFT GAs TURBTNE POWER PLANTS 2SHEETS-' SHEET l Filed July 19, 1945 k3b max, IR, Erm. w1 Rl l mw :sof.BSK ALI:

Inventors'.

w d E A Dojn ald E. Barr,

e n f A A@ .m u e H .n T

Dec. 23, 1952 M. A. EDWARDS ET Al. 2,622,393

FUEL REGULATING APPARATUS FOR AIRCRAFT GAS TURBINE POWER PLANTS FiledJuly 19, 1945 2 SHEETS-SHEET 2 TW Martin ,Mdwarctgh MO le,.

Donald B Gar HU by -W Their` Attorney Patented Dec. V23, 1952 FUELREGULATING APPARATUS FOR AIR- CRAFT GAS TURBINE POWER PLANTS Martin A.Edwards, Scotia, and Donald E. Garr and Hugh M. Ogle, Schenectady, N.Y., assignors to General Electric Company, a corporation of New York vApplication July 19, 1945, Serial No. 605,960

(Cl. (l-39.28)

12 Claims.

The present invention relates to gas turbine power plants and controlmechanism therefor, and is of particular significance in connection withturbines for jet propulsion of aircraft. Aircraft gas turbines presentdifficult control problems due to the various changes of operatingconditions to which they are subjected. These variations cover wideranges of ambient atmospheric pressure, temperature, speed, and load,necessitating correspondingly great changes in the rate of fuel supply.Ordinarily the lowest fuel supply is needed during idling operation athigh altitude, and the maximum fuel supply is required for full power atsea level.

An object of our invention is to provide an improved control system fora gas turbine powerplant. Another object is to provide a controlmechanism for varying the rate of fuel supply in such a powerplant inresponse to changes in a combination of various operating conditions. Afurther object is to provide improved components of such controlmechanism whereby efficient control, safe operation, and long life ofthe powerplant are assured.

Further objects and advantages will be apparent from the followingdescription and the claims appended thereto taken in connection with theaccompanying drawings, in which Fig. 1 illustrates a gas turbine jetengine for aircraft with a fuel system arranged and controlled inaccordance with our invention; and Fig. 2 is a diagrammatic perspectiveview of the control mechanism for the fuel system shown in Fig. 1.

The powerplant of Fig. 1 comprises the housing I containing an aircompressor, which may be of the multistage axial flow or centrifugaltype. The casing l has an inlet 5 arranged to receive air from suitableintake openings in the engine nacelle (not shown) which openings mayface in the direction of night with the passage to the inlets 5 arrangedas a diffuser to convert part of the dynamic pressure of flight intostatic head at the inlets 6. The air is compressed as it passes throughthe compressor and is discharged into a plurality of combustion chambersor combustors 8 circumferentially arranged about the axis of the engine.The ccmbustors may be of the type disclosed in application for patentSerial No. 501,106, filed on September 3, 1943, now abandoned, and inPatent No. 2,601,000 (a continuation-in-part of application Serial No.501,106) in the name of Anthony J. Nerad and assigned to the sameassignee as the present application. Fuel is supplied by a nozzle I3projecting into one end of each combustor land connectedto fuelmanifolds i2 and Ill. Because of the wide range of operating loads to beobtained, the fuel-burning system is of a type adapted to provide a rateof fuel flow which changes as a predetermined function of the fuelpressure, at the inlet point 9 to the burner system, over a wide rangeof pressures. The fuel burning system shown comprises a directconnection 2 from the main fuel supply conduit 30 to the high pressuremanifold it, a second connection l through a pressurereducing valve orflow divider 5 to the low pressure manifold I2, and suitable branchconnections 'l from the manifolds to the respective fuel nozzles I3.Drip valves 26 and 21 are provided at the lowest points in the high andlow pressure manifolds, respectively, and are arranged to automaticallyopen and drain the fuel manifolds through conduits 2l when the enginestops and the pressure in the fuel system drops to a preselected minimumvalue. This fuel-burning system is more fully disclosed in anapplication Serial No. 622,604 filed in the name of Charles D. Fulton onOctober 16, 1945, now Patent No. 2,590,853, and assigned to the sameassignee as the present application.

Hot gases from the combustors 8 pass to a gas turbine in the housing I5,whence they pass through the cone I8 to the tailpipe I9, which leads toany suitable type of propulsion nozzle Illa. The gas turbine is ofcourse arranged to drive the air compressor. The details of thecompressor, combustors, and turbine are not necessary to anunderstanding of the present invention, particular arrangements beingmore fully described in other applications, specifically Serial No.541,565, filed June 22, 1944, and Serial No. 506,930, now Patent No.2,479,573, ledOctober 20, 1943, in the name of Alan Howard, and SerialNo. 525,391, now Patent No. 2,432,359, i'lled March 7, 1944, in the nameof Dale D. Streid.

At the forward end of the engine is an accessory drive gear casing I6provided with a number of projecting splined shafts for driving variousengine accessories secured to the front of the casing I6. Theseaccessories may include many not shown in Fig. 1, such as an electricgenerator, starter motor, ignition devices, hydraulic power pump, vacuumpump, tachorneter drive, and various other electrical and hydraulicmechanisms. Such an accessory drive section is disclosed in anapplication Serial No. 525,389, now Patent No. 2,432,358, led March 7,1944, in the name of Donald F. Warner and assigned to the sameassigneeas the present application.

Mounted on one of the accessory drive pads is a fuel pump 28 having aninlet conduit 2S connected with the main fuel tank. 2i@ and a dischargeconduit E@ carrying the main fuel supply through a shut-ofi` valve orstopcock 2l to the point 9 at which the fuel enters the fuel-burningsystem referred to above. The pump 28 is illustrated as being of thevariable stroke positive displacement type. The pump displacement isvaried by a control mechanism or regulator Si also mounted on theaccessory drive casing it and receiving oil or like operating fluidunder pressure from a second positive displacement pump 32, which has aninlet 33 for connection to a source of control oil and discharges into aconduit 315 connected to the regulator 3l. Both the fuel pump 28 and thecontrol oil pump 32 are driven by the turbine through the gearing incasing i6.

The fuel supply to the nozzles i3 inthe.com bustors S is caused to varyby the action of the regulator 3l in. response to changes in severaloperating conditions, as will be more fully described hereinafter.

Oil pumps As previously pointed out, the fuel rate in a gas turbinepowerplant of the type described must be varied continuously over a widerange, of the order of l to. 20, from idling to full load operation.Such performance may be obtained with a variable stroke positivedisplacement pump such .as pump ES (see Fig. 2), which comprises acasing S forming a plurality of circumferentially spaced axial cylinders3S each accommodating a reciprocating piston 37.. The outer ends of thepistons are engaged by a wobble member 38'. The angular relation of themember 38 to the aXis of' the pump is controlled by a servomotorincluding a piston 39 having a rod connected to the member St andslidably disposed in a pressure chamber [it formed in an enlargedextension of a shaft lil. Shaft s! has a central bore. d2 connecting thepressure chamber A@ to a pipe life, which latter is connected to acontrol valve ai, the function of which is to vary the pressure of oilin the chamber dfi. Supply of oil to the chamber di! by valve d@ forcesthev piston 39 outward, thereby increasing the angularity of wobblemember 38 and increasing the. stroke of the pistons and the displacementof .the pump 28. Upon draining of liquid from the .chamber dil, theangularity of the wobble member is decreased. The flow. becomes zerowhen the driving face of the wobble member is perpendicular to thesha-ft 4I and the angularity szero. Wobb'le member 38 is biased againstthe oil pressure inv chamber it by a helical spring 'surrounding thecasing 35, bearing at its righthand end against a flange of the casingand at its left-hand end against an axially s'lidable ring 46. The inletconduit 251i of the pump communicrates with an annular channel d? havinga pluralityr of axial ports which establish connection with certain ofthe cylinders during a portion of the cycle of operation, while thedischarge conduit Sli-is connected by similar ports and another annularchannel i8 of the pump to the remaining cylinders from which liquid isdischarged during the same part of the cycle. It will be understood bythose skilled in the art that the pump shown in Fig. 2 is merely adiagrammatic representation of one type of variable positive`displacement pump which is well known, and

other suitable pumps of this type can be used as Well.

Abypass conduit 3S? including a pressure relief valve au prevents fuelpump discharge pressure from exceeding a predetermined safe value.

The device for controlling the stroke of the pistons Si comprises acasing i having an inlet port 5I for receiving high pressure oil fromthe supply conduit 31-- a-nd another port connected to la conduit 52`for receiving oil from regulator 3! under a variable control pressure.The pressure of the oil in conduit 34 is relatively constant at forexample 259 lbs. per square inch (except lfor slight variations due tothe character-isticsof pump 32 and valve lil), whereas the controlpressure oil in conduit 52 varies with 'varying operating conditions, aswill be described hereinafter.

Bushing 53 is slidably disposed in the casingiiiA and has axially spacedports 5d andi controlled by valve discs 5S and 5l' secured to a rod 58'.In the position shown, head 55 coversth'e port M, thhereby interruptingcommunication between the high pressure line 3e andthe conduit d3leading tothe pressure chamber @t for controlling the fuel pump. YThehead 5l' and .the casing form a control pressure chamber 553 `connectedto the conduit 52. The force of the fluid pressure in they chamber. 59against thevalve head.- 5'i is opposed by a pressure-sensing piston 6!in cylinder @il and connected to an extension of the valve rod 5t. Thecylinder 'til is connected to the discharge conduit 3U of the fueisupply pump so that piston 6l is responsive to gage pressure of the fuelin conduit 3d. Piston 6| and the valve member 55, 5l, 53 are. biasedyinto a neutral position by two Yopposed centering springs 62 engagingopposite faces -of the piston 5i and the valve head El. Bushing 53 ispivotally connected to a followup lever t3 which has an intermediateportion held on a nized fulcrum and an end portion enthe axiallyslidable ring dii of the fuel pump. The control valve Se has a reliefconduit 55.1 which is connected for convenience to the casing ofregulator Si, from which oil drains by conduit "il baclr to the controloil reservoir During steady state conditions the fuel supply pressuresensed by the piston l in the cylin- -der Bil balances the pressure inthe control chainber 5t of the valve, and the valve disc 56 covers theport leading to the conduit 43. For any giveny set of voperatingconditions, the pressure in the control cylinder 4l? of the pump remainsconstant. Upon increase of the control pressure in chamber Eis, thevalve discs are forced to the left against the pressure in the cylindercaus ing flow of control oil from the conduit 3d Vthrough the conduit5i, valve dit, conduit 43, and

the bore d2 of the pump shaft, into the chamber da, causing movement ofthe wobble member 38 te increase the stroke and accordinglyy thedischarge pressure of the pump 2B. This increased discharge pressure iscommunicated to the cylinder 6% where the piston 6i moves to the right,causing the valve disc ist to assume its original line-in-line positionwith the port 511i.

Thus it is seen that the piston El provides follow-up action for thecontrol valve member 55, 5l', 58. However, the time lag between a changein pressure in the chamber 59 of the valve and the restoring movement ofpiston 5i may cause hunting and instability of operation. The

lever B between the bushing .53 of the valve and the ring` :l5 of thepump constitutes direct mechanical follow-up means for reducing theeffective time lag, thereby preventing hunting.

Asl pointed out above, the movement of the val-ve disc 5t to the left,causes increased stroke of the pump pistons, effected by increasing theangularity of the wobble member 38 whereby the latter forces the ring 48toward the right against the biasing force of the compression spring 45.This in turn permits counterclockwise movement of the lever `53 aboutits fulcrum under the biasing influence of the pressure in chamber 59acting on the end of bushing 53, whereby the latter is moved toward theleft to effect at least partial restoring of the original relativeposition between the valve disc 58 and the port 54 in the bushing.Normally bushing 53 is held stationary by the lever 63, which preventsit from mo-vement toward the left by the fluid pressure in the chamber59 acting against the 'right-hand end of the bushmg.

It will be seen that fuel pump 28 and its control valve 44 constitutemeans for delivering liquid vfuel to conduit 38 at a pressure which is apredetermined function of a variable control pressure supplied to thevalve 44, the relation between the two pressures depending on theproportioning of the pistons 51, 6| and the characteristics of springs62.

Control oil is supplied to the valve 44 by the conduit connected throughpipe 34 to the discharge side of control oil pump 32. The latter may beof the well-known gear type, as shown in Fig. 2, and may be driven fromthe shaft 4| of the fuel pump 28. The inlet conduit 33 of the controloil pump is connected to a reservoir 88. In order to prevent excessivepressures in the discharge conduit 34, a bypass 59 with a pressurerelief valve 18 is provided between the conduit 34 and the tank G8.

Regulator Referring now to the regulator for establishing the controlpressure in the chamber 59, a number of distinct condition-responsivecontrol devices are provided to vary the control pressure automaticallyin response to changes of certain operating conditions, as well as othermechanism for manipulation by the operator to select the load output ofthe powerplant. The automatic control means act to maintainsubstantially constant the load output selected by the operator whilesafeguarding the engine from overspeed and excessive temperatureconditions.

Manual control As may be seen in Fig. 2, the manual control mechanismcomprises a main control lever 12 having lan intermediate portionsupported on a pivot 13. A lever portion above the pivot 13 is engagedby aV manually adjustable cam 14 secured to a shaft 15, which latter hasan end portion connected by an arm 18 (see Fig. 1) to a link 11 formanipulation by the operator or pilot through hand lever 22, link 25,and lever 24, which latter is pivoted on fulcrum 3. Movement of the handlever 22 causes rotation of the cam 14, effecting turning movement ofthe main control lever 12 about the pivot 13. The lower end of the lever12 is held in engagement with a control and follow-up lever 18 by theaction of a tension spring 19 connected to the lower end of the lever12. Lever 18 has an intermediate slotted portion connected to a stem 80of a hydraulic motor 8| controlled by a pilot valve 82 having an inletport 83 connected to the control oil supply conduit 34 and a drain port84 discharging into the casing 65. Pilot valve 82 rhas discs 85 securedto a stem 86 connected to the left-hand end of the lever 18 and biasedtoward theright by a tension spring 81. The discs 85 normally are inaligned position with the respective ports 83, 84. A third port 88 islocated between the discs and connected to the conduit 52 which latterhas a branch 89 connected to the pressure chamber of the servomotor 8|.The stem 88 with the piston of the servomotor 8| are biased against thefluid pressure in the servomotor by means of a tension spring 98 actingon the piston through a variable moment arm arrangement 9| describedmore in detail hereinafter. For the present it is sulcient to note thatthe force produced by the servomotor 8| on rod 80 is balanced by a forceproduced by the spring 98.

During operation a pull on the manual control link 11 causes decreasedfuel supply and accordingly decreased speed and output of the engine.More specifically such pull on the link 11 causes counterclockwiseturning movement of the cam 14, thus forcing the main control lever 12clockwise about its pivot 13, against the biasing force of the spring19. The lower end of the lever 12 tends to move away from its engagementwith the lever 18. The engagement between the levers 12, 18, however, ismaintained by action of the spring 81 which turns the lever 18 clockwiseabout its pivotal connection with the stem 88. This causes movement ofthe pilot valve discs 85 to uncover the drain port 84, permittingdischarge of fluid from the hydraulic motor 8| and the pressure chamber59 through the conduits 89 and 52, resulting in decreasing pressure inthe pressure chamber of the motor 8| and the control pressure chamber 58of the valve 44. Decreasing pressure in the valve chamber 59, asexplained above, causes decreased discharge pressure of the pump 28 andaccordingly decreased fuel ow to the combustors 8. Decreased pressure inthe servomotor 8| causes the piston to move toward the left by action ofthe spring 98, whereby the lefthand end of the lever 18 electsrestoration of the aligned position of the valve discs 85. Similarly, apush on the link 11 causes clockwise turning movement of the cam 14,effecting operation of the various elements in a direction opposite tothat described before, resulting in increased fuel supply to thecombustion chambers.

The manual control mechanism thus comprises a fluid pressure motorhaving a pilot valve positioned by the operator to impart to valve 44 acontrol pressure corresponding to the desired output.

Speed control Speed control means are provided to take over control ofthe powerplant upon increase of the speed above a preselected value. Inthe present embodiment, this speed control comprises a centrifugal speedresponsive device including flyweights 92 pivotally held on fulcrums 93secured to a gear 94. The latter meshes with a gear 95 secured to agovernor drive shaft 98 driven by a stub shaft projecting from the gearcasing I8. Flyweights 92 operate a pilot valve 91 for controlling 'aspeed sensing cylinder 98. The pilot valve 91 has a stationary casing Q9with spaced openings connected to the pressure supply line 34 and to aconduit |88 which has another end connected to the cylinder 98. Abushing |8| is slidably disposed in the casing 89 and at its lefthandend prcvided with a flange engaged by the flyweights 32. rlhe right-handend of the bushing is engaged by a variable compression spring |02 whichat its right-hand end bears against a Y7 thev top surf-ace of the capand are. arranged to be positioned by rotation of the shaft 23. Thebushing, IUI has two spaced ports communicating with line 3d and theconduit Idil respectively and controlled by valve dises |65 secured torod Iii@ which at its right-hand end is pivotally connected to a leverll by means of a slot connection. The lever lill is ulcrumed at itsupper end on a pivot Hi8. The lower end el the lever is biased b-y acompression spring itil' against the right-hand end of the stem It ofthe motor 98. The stem Iii? is connected to the main control lever 'l2by means of a beller-ank lever rotatably supported on a pivot ||I andhaving a forked end I|2 associated with an abutment H3 on the stem lIand another arm i I4 with an adjustable threaded pin i5 arranged `toengage the main control lever l2.

During operation on direct manual control through cam lil', the speedgovernor being ineffective (as shown in Fig, 2), bushing lui will be atthe extreme left end of its range of movement, so that liquid from motori will be drained to the left of piston lil-5 and through port IGI tothe interior of casing E55, thus preventing displacement of the pistonin servomotor 9d, Upon an increase in speed the flyweights t2 moveoutward under centrifugal force, thereby pushing the bushing mi to theright against `the biasing force of the spring |32. Movement ci thebushing Il to the right establishes communication between the ports ofthe bushing, thus causing the flow of oil from the supply line 3'. intothe conduit Edil and the pressure chamber of the motor 9s. The pistonoi' the motor $33 is thereby forced to the right, causingcountercloclnvise turning movement of the bellcrank about the pivot andmoving the pin l I5 toward the main control lever 52, While theconnection between lever il? and rod ille results in restoration of thepilot valve to shut ofi the supply of liquid to motor d8. At apreselected speed the pin I i5 engages the lever i2, and upon. furtherincreasing speed moves the lever I2 away from the cam ifi. Thus at apredetermined speed the governor takes control of lever away from thedirect manual control means 'iai- 1?.

As the main control lever 'i2 is moved away from the cam 'ifi the pilotvalve 83 is actuated to cause discharge of oil from the pressure chamberof the motor 8| and from the chamber 59 of the valve lill, resulting indecreased fuel supply to the ooinbustors in the manner explained above.Upon movement of the stem Ilo of the servomotor 9S toward-the right, thelever |57 is turned counterclockwise about the pivot ldd and therebyrestores the pilot valve discs I to their original position relative tothe ports in the bushing.

Upon decreasing turbine speed the operation is similar to that describedabove, with the various elements moving in opposite direction andproducing increasing fluid flow to the combustors. With decreasingspeed, the lever 'l2 moves counterclockwise and engages the cam lil; andupon further decrease in speed the threaded pin H5 moves away from thelever l2, the speed governing mechanism thereby being renderedineffective and the control of the plant being transferred back to thedirect manual control mechanism (and the other control devices describedhereinafter) Temperature control The eiliciency, economy of operation,and life of a gas turbine powerplant vary considerably With theoperating temperatures. K We have discovered that a practical andsatisfactory criterion of the general temperature level at which anaircraft gas turbine jet engine is operating is the temperature of thegases discharged from the turbine. In general, the efficiency andeconomy of the jet engine increases with increasing temperature level,while the life decreases. Hence, it is desirable to operate Such apowerplant at the maximum safe temperature level consistent with therequired life expectancy. This is accomplished in accordance with ouri-nvention by the provision of means permitting operation up to apredetermined maximum temperature of the turbine exhaust gases butpreventing operation at temperatures above that value in order toprevent excessive stresses and premature deterioration of the variousstructural elements of the powerplant.

In a preferred embodiment, temperature control means are provided whichinclude mechanism arranged to act on the main controlv lever 'I2 througha lost motion connection so as to be normally ineffective and renderedoperative only as the limiting temperature is exceeded. Upon exceedingthe temperature limit it is desirable in the interest of safety that thethermal means quickly take over control of the fuel supply and effect arapid decrease in fuel pressure; Whereas upon decrease in temperature itis desirable in the interest of stability to increase slowly the fuelsupply to the combustion chambers, so as to prevent too rapid anincrease in temperature with the accompanying danger of overshooting thelimiting value.

The means shown in the drawings for accomplishing these objects includesa thermal unit il'n secured in the tailcone I3. While only one thermalunit is illustrated in the drawings, it Will be understood by thoseskilled in the art that several similar units, circumferentially spacedand connected in parallel, may be used to obtain an indication ofaverage temperature over the entire cross-section of the tailcone. Thethermal unit is connected to an inlet conduit I and a discharge conduit||8 emptying into the regulator casing S5. rlhe function of the thermalunit (or units) is to establish a control pressure for a temperaturesensing cylinder H9 (Fig. 2) having a spring-biased piston |26 connected.by lost motion means to a bellcrank I2| fulcrumed on a pivot |22 andhaving one arm associated with a U-shaped member |23 secured to the endof the stem of the servomotor I I9. The other arm of the bellcrank has athreaded pin |24 adjustably secured to its end and arranged to engage`the main control lever 72. The pressure chamber of the servomotor IIS:is connected by a conduit |25 to conduit Il.

Control oil under pressure is supplied to the conduits |25 and I Il fromthe supply conduit 34 through a rotary flow limiter |26 comprising aportion of the shaft S6 with an axially extending slot l2? disposedWithin a stationary sleeve |28. Axlally spaced portions of the sleeveare connected to the conduits 3d and ||7 respectively. During rotationof shaft 56, the slot |27 elects periodic communication between theconduits 34 and lil. The rotating slot |21 and the ported sleeve |28constitute a rotary restrictor presenting a resistance to the iloW ofliquid from thei supply conduit 34 to the conduits |25, II'I whichresistance depends primarily upon the length and Width of the slot |21.This rotary ovv limiter has the very great advantage of produclng adesiredfeiiective resistance to now without resorting to smallflow-limiting orifices which might become fouled by dirt in the controloil. The rotary ow limiter is not subject to this danger because thepassages are all of relatively large cross-section. While the slotconnects the conduits it permits substantially free ow therethrough. Therestriction of the flow is due to the rap-id successive periodicinterruption of the flow path between the conduits 34, ||1. It will beunderstood that the speed of rotation of shaft 96 is suiiciently greatthat the average rate of ow past the rotary restrictor is substantiallyconstant.

The flow of fluid from the conduit 34 into the conduit ||1, andaccordingly the pressure in the pressure chamber of the servomotor I9,is determined by operation of the thermal control means IIB. The device||6 comprises means responsive to temperature changes and a valveassociated with the conduit ||1 for controlling the oil iiowtherethrough. More specifically, the temperature-responsive means in thepresent example includes an outer tube |29 and an inner rod |30centrally disposed within and suitably secured to the lower end of thetube |29. The tube and the rod are made of materials having differentcoefcients of expansion. For example, the tube |29 may be of a suitablehigh temperature metal such as Nichrome and the rod |30 may be of fusedquartz. The upper end of the metallic tube |29 is secured to a iiange|3|. The inner rod |30 is provided with an extension |32 sealed to thecasing |3| by means including a bellows |33, the lower end of thebellows being sealed to the casing |3| The upper end of the extension|32 projects into a chamber |34 and engages a lever, in the presentinstance in the form of a cantilever spring |35 which has a right-handend engaging an adjusting screw |36 and a left-hand end engaging aplunger |31. The member |31 is associated with an outlet |38 of theconduit H1. Movement of the member |31 toward the outlet |38 increasesthe resistance to flow of fluid therethrough and thereby increases thepressure within the conduit ||1, and also in the chamber of thetemperature-sensing servomotor |19. Conversely, movement of the plungerfrom the outlet |38 reduces the resistance to flow from the outlet |39and accordingly reduces the pressure in the conduit ||1 and the pressurechamber of the servomotor H9. Control oil discharged from conduit ||1into chamber |34 is drained through conduit ||3 back into the regulatorcasing 65, thence through pipe 1| to tank 68.

Upon increase in temperature the metal tube, having a higher coefficientof expansion than the inner quartz rod |30, expands downwardly, andthereby causes -collapsing of the bellows |33. This effects downward oropening movement of the plunger |31, resulting in decreased pressure inthe servomotor H9. The spring-biased piston |20 thereupon moves to theleft causing counterclockwise turning movement of the bellcrank which ina certain predetermined position engages the main control lever 12, andupon increase in temperature thereafter the thermal device takes overthe control of the engine.

As previously pointed out, clockwise turning movement of the maincontrol lever 12 about the pivot 13 effects decreased fuel supply to thecombustion chambers, while counterclockwise movement results inincreased fuel supply. In case of rising temperature, a quick controlaction takes placewbecause opening Vor downward movement of the plunger|31 causes quick emptying or relief of the pressure in the chamber ofthe servomotor |9 through the conduits |25, |1. It is important to notethat in this action the rotary restrictor |20 has no effect on the rateof response of the thermal control because the restrictor is outside theuid circuit connecting the temperature sensing cylinder I9 and thethermal device H6. On the other hand, upon decreasing temperature, whenthe plunger or valve member |31 is moved toward the outlet |38, there isa less immediate response of the piston |20, because such movementrequires rst the supply of control oil from the conduit 34 through pipe|25 into the cylinder H9, which supply is retarded by the ilow'restrictor |25. Thus there is obtained a slow response of thetemperature control mechanism with decreasing temperature, as comparedwith the prompt action produced with increasing temperature.

The tailpipe or turbine discharge temperature at which the thermaldevice takes over control is a function of the load output selected bythe manual control mechanism. The higher the load setting selected bythe operator, the lower the temperature at which control is taken overby the temperature-responsive mechanism, because with increasing loadthe amount of lost motion between the main control lever 12 and thebellcrank |2|, |24 is reduced. Hence, the point at which the thermaldevices take over control is a function of both turbine dischargetemperature and the load setting. This is necessary because the primepurpose of the thermal control is to prevent excessive temperatures ofcritical parts,

particularly the turbine bucket-wheel; and the mean turbine temperaturesare a function of inlet temperature, pressure drop across the turbine,and various other minor factors such as reheat in the turbine bucketpassages due to friction losses. It has been found by experience thatthe turbine discharge temperature is a satisfactory and reliableindication of the mean powerplant temperatures when thus modified inaccordance with the load setting, which latter may be considered torepresent a measure of the tem- -perature drop across the turbine.

For a given load setting the temperature control mechanism may beadjusted by positioning the threaded pin |24 on the bellcrank or bypositioning the screw |30 of the thermal device H6. It should be notedthat the critical temperature, at which the thermal device becomeseffective, varies only as a function of load setting, since, asdescribed elsewhere herein, a given position of the lever 12 correspondsto a given load settingY regardless of altitude.

It is to be noted that the pressure of the control oil supplied to thethermal device from conduit 34 may not be entirely constant duringoperation. However, the spring-biased piston |31 acts as a pressureregulating device to hold the pressure in line ||1 (and servomotor H9)constant, so that the pressure will vary to actuate thetemperature-responsive piston |20 onlyV when the thermal device |34dictates a change in pressure.

It may be noted that the vvariations of the pressure in line ||1 havethe effect of preventing sticking of piston |31.

To summarize, our invention includes a control means responsive totemperature changes of the turbine exhaust gases for taking over controlof the powerplant at a preselected maximum safe temperature, thecritical temperatureY being a function of the output, increasingwithdecreas-- ing load and vice versa. The arrangement includes meanseffecting rapid response by the temperature-responsive mechanism uponincrease in temperature but effecting a slow control action upondecrease in temperature.

Altitude control The efficiency of a gas turbine powerplant is afunction of a number of factors, an important one being the energy levelat which the turbine operates. Generally eiiiciency increases withincreasing initial turbine temperature and with increasing pressure dropacross the turbine. The turbine nozzlebox pressure and temperature in ajet engine of the type referred to herein is a function of the rate offuel supply and the compressor discharge pressure; while the turbineexhaust pressure is a function of altitude, decreasing with increasingaltitude. Therefore, it will be seen that efficiency and output wouldvary with altitude unless suitable compensating means were provided. Animportant feature of our invention is the provision of means forrecalibrating the regulator in response to changes of some pressureappurtenant to the operation of the powerplant, which pressure varies asa function of altitude. Furthermore, with increasing altitude vtheover-all eiiciency of a jet-propelled aircraft having a gas turbinepowerplant increases by reason of decreased drag and other factors;therefore, at high altitude less fuel is required for a given propulsioneffect than at low altitude. According to our invention mechanism isprovided responsive to changes of a pressure which varies as a functionof altitude for varying the fuel rate.

This altitude responsive mechanism comprises a device responsive tovariations in absolute atmospheric pressure, and includes an evacuatedbellows |39 held at its left-hand end on a xed support |40 and connectedat its right-hand end to a rod IM pivotally connected to an intermediatepoint of a lever |42. A second bellows M3 is secured vat its right-handend to a xed support |435 and is connected at its left-hand end to anextension of the rod Uil. Bellows ist is biased against expansion by acompression spring |55 between its left-hand end and a xed support M5.The interior of the bellows |43 communicates through a conduit lill withthe altituderesponsive control pressure, which may be either ambientatmospheric pressure or the discharge pressure of the compressor. Atpresent we prefer to use compressor discharge pressure, which in apowerplant of the type illustrated is a function of ambient altitudepressure, ram pressure of flight (i. e. airspeed) and compressor speed.The bellows are of equal eifective areas so that the common pressure incasing 55 acting on the exterior of both bellows alike has no net effectand the rod |4| is moved only in response to changes of thev absolutevalue of the pressure communicated through conduit ll to the interior ofthe bellows The upper end of lever M2 is biased by a spring |48 andforms a pivotal connection with the stem |49 of a pilot valve |55 havingvalve discs |5| secured to the stem |69 and cooperatively associatedwith two ports. The right-hand port is connected to the control oilsupply line 54, and the left-hand port is connected by a conduit |52 toa rotary ow limiter |53 (which is similar to the device |26) having aslot |54, an inlet port |55, and a drain port |56. The pilot valve |55is connected between its aforementioned ports by a conduit |57 to thepressure chamber of aservof motor |58, which includes a spring-biasedpiston |59 connected to a stem |55. The lower end of the lever |542 isbiased by the spring |48 into engagement with a transverse pin on thestem |65.

Upon increasing altitude, the bellows U53 collapses causing clockwisemovement of the lever |42 about its connection with the stem |65 byreason of the bias of spring M38, whereby the discs |5| of the pilotvalve |50 are moved to the right, admitting high pressure fluid from theconduit 35 into the conduit |5'l to increase the pressure in the chamberof the servomotor |58, and resulting in outward movement of the piston|59. This effects follow-up movement of vthe pilot valve bycounterclockwise turning movement of the lever 52 about its pivotalconnection with the rod lill, resulting in restoring movement of thediscs |5| into aligned position with their respective ports.

It is important Yto note that upon decreasing pressure in bellows |53(increasing altitude). the piston |55 moves quickly, the pressure in itschamber being quickly increased because the conduits 3ft, |5`| are freefrom any restriction to iow. On the other hand, upon increasing pressure-in belows |53 (decreasing altitude) the various elements are moved inthe opposite direction. The valve discs |5| uncover the connection withthe conduit |52, causing draining of fluid from the chamber of theservomotor |55 through conduit l5?, pilot valve |55, conduit |52,restrictor |53, and drain port |55. The flow restrictor |53 retards thisdischarge of fluid from the servomotor |58 and consequently causes slowaction of the altitude responsive mechanism upon increasing pressure inbellows ili (decreasing altitude).

The servomotor piston |59 is arranged to vary the fuel pump outletpressure and in View of the action just described causes a comparativelyrapid drop of such outlet pressure upon decreasing pressure of theatmosphere and a slow rise of the outlet pressure upon increasingpressure of the atmosphere.

A feature of our invention is the variable lever assembly 9| connectedbetween the stem 80 of the servomotor 3|, the spring 59, and the pistonrod |55 of the servomotor |53. Broadly, this variable ratio lever deviceincludes two levers connected together by an adjustable fulcrum, whichlatter is positioned by the servomotor |53 of the altitude responsivemeans.

More speciiically, the variable lever mechanism comprises a first leverll fulcrumed at its left-hand end by means of a pivot |52 and connectedat its right-hand end to the spring 9i! by means of an adjustablethreaded rod |53. A second substantially parallel lever |55. ispivotally connected at its left-hand end to the stem t@ and is at itsright-hand end held against a roller |55 mounted on a xed axis. Thepivotal connection between the rst lever |5| and the second lever |64 isaccomplished by means of a shaft |55 carrying an intermediate roller |61and two outer rollers |58. The intermediate roller |57 bears against thelever |64 and the outer rollers |58 bear against depending edge portions|59 of the first lever |6|. The shaft |56 is connected between the armsof a fork l'l which at its left-hand end is pivotally connected to thestem |56 oi the servomotor |58. With this arrangement the force of theVspring 9c is transmitted through the first lever IGI to therollercarrying shaft |68, to the second lever |54 and thence to the stemof the servomotor 8|.

13 With the roller-carrying shaft or movable fulcrum |66 in a fixedposition the operation of the servomotor 8| is the same as that of anordinary servomotor having a piston biased by a spring of a suitableforce.

At shut-off pressure, defined as the pressure in the control chamber 59when the stopcock 2| just closes, i. e. when fuel pressure at station 9drops to zero, the levers |6|, |64 are exactly parallel to each otherand to the path of movement of variable fulcrum |61. In this condition,movement of the fulcrum |61 will have no effect on rod 89. Therefore thepressure in control chamber 59 corresponding to zero fuel pressure issubstantially constant regardless of altitude. When the control pressureis at any value above shut-off pressure, the levers |6I, |64 are at anangle to each other, and to the path of movement of the variable fulcrum|61, so that movement of the fulcrum recalibrates the regulator asdescribed hereinafter.

With our arrangement the variable fulcrum |66, |61, |68 is positioned inresponse to changes of a pressure varying as a function of altitude.Upon increasing pressure in bellows |43, servomotor piston |59 moves tothe left and thereby moves the variable fulcrum toward the left,increasing the effective moment arm between the spring 90 and the stem88 of the servomotor 8| and producing a slight inward movement of thepiston of the servomotor 8|, thereby increasing the pressure in thecontrol chamber 59 of the valve 44. This increase in pressure in theservomotor 8| is further aided by movement of the pilot valve disc 85 toadmit iiuid pressure from the supply pressure conduit 34 to theservomotor 8| and the control pressure chamber 59. Increasing pressurein the chamber 59, as explained before, results in increased fuel supplyto the combustors and accordingly increased output of the powerplant.Also, the supply of fluid under pressure from the conduit 34 through thepilot valve to the servomotor 8| forces its piston Y back outward,thereby restoring the pilot valve discs 85 to their original alignedposition with their respective ports.

Conversely upon decreasing pressure in bellows |43, the variable fulcrum|66, |61, |68 is moved toward the right, that is, toward the fixed pivot|65, causing outward movement of the piston of the servomotor 8| and ofthe valve discs 85 whereby fluid is drained from the port 84 of itspilot valve, resulting in decreasing pressure in the pressure chamber ofthe servomotor 8| and the control chamber 59 of the valve 44 and.decreasing outlet pressure of the fuel supply pump 28.

The adjustment of the variable fulcrum |66, |61, |68 has the effect ofrecalibrating the force of the spring 90, the force being increased withincreasing ambient atmospheric pressure and decreased with decreasingatmospheric pressure. This adjustment of the force of the spring 9|) byaction of the altitude responsive control has the additional effect ofrecalibrating the manual control mechanism, of which the spring 90 alsoforms a part. The variable lever 9| and the manual control linkage areso arranged that the full travel of the operators control handle 22(Fig. 1) from closed to open position always corresponds to full rangeof engine output from idling to full load, regardless of altitude. Themaximum safe output, that is, the

full load rating of an aircraft gas turbine jet 14 engine varies withaltitude; and the variable lever mechanism 9| is also so designed thatwith the manual control handle 22 in a given position the powerplantwill maintain a substantially xed percentage of the full load output atvarying altitudes. The force of spring may be adjusted by means of thethreaded pin |63 attached to the spring 90.

Thus it is seen that the altitude control includes means for varying thefuel pump discharge pressure in response to changes in a controlpressure which is a function of altitude by varying the effective momentarm of a biasing force, the mechanism including a rotary flow restrictorarranged to effect slow response upon decreasing altitude and quickaction upon increasing altitude.

The manual, speed, and temperature control means described above may beinoperative under particular operating conditions; but the altitudecontrol is effective at all times to modify simultaneously the action ofeach of the other control devices.

Operation The coordinated operation of the complete control systemoutlined above may be described briefly as follows.

All controls for the fuel system are integrated by means of suitablelinkages connecting the various control devices to the single operatinghandle 22 (Fig. 1), which actuates the main control lever 24 throughpushrod 25. From a comparison of the linkage shown diagrammatically inFig. 1 with the components of the regulator shown in Fig. 2, it will beseen that manual con trol for the regulator 3| is effected through shaft15, lever 16, and link 11. Recalibration of the speed governor iseffected through shaft 23, carrying lever 23', which latter is connectedto link IB through a pin-and-slot lost motion connection Stopcock 2| isactuated by lever 2| secured to the shaft 3 on which the main controllever 24 is mounted.

It should be noted that in Fig. 1 the throttle 22 and quadrant 22 areenlarged somewhat out of proportion to the remainder of the controllinkage.

The above described linkage is so proportioned that as the controlhandle 22 is moved from the closed position, the stopcock 2| is quicklymoved to full open position, say during the first l0 degrees ofmovement. During this movement the regulator shaft 15 moves, but thegovernor shaft 23 is permitted to remain stationary by the lost motionconnection During the first 20 degrees of movement from the completelyclosed position, rotation of the shaft 15 counterclockwise operates toset the regulator by positioning lever 12 through cam 14 to call for anincreasing fuel pressure at the point 9, and the speed of the enginerises to approximately 2600 R. P. M. (about 35 per cent of rated fullload speed). During this first 20 degrees of travel the speed governorsetting remains unchanged by reason of the lost motion connection Il, tohold the speed constant at 2600 R. P. M. If for some reason the speedshould increase above 2600 R. P. M., the speed governor will operate toreduce it to that value; but as long as the speed remains below 2600 R.P. M. the speed governor is inoperative with the control handle setanywhere within the rst 20 degrees of its movement, and regulation ofoutput is by manual control acting directly on lever 12 through cam 14.

As the control handle passes the 20 degree position, the lost motion inthe connection H is taken up and further movement of handle. 22 servesto act through link 23' and shaft 23 to change the speed governorsetting. From the 2li degree position to the full open position ofthrottle 22, manual control of the engine is effected by recalibrationof the speed governor. During such operation, the manual control cam 'i4on the shaft does not touch the lever l2, but follows movement of thelever 'l2 with a slight clearance therebetween. With this arrangementthe manual control cam 'M is always in a position to immediately takeover control of the engine in the event the speed governor fails.

It will be obvious to those skilled in the art that the coordinatinglinkage of our control system could be so arranged that as thehandle 22moves from the closed position, rst the stopcock is opened wide, thenthe manual control through shaft 15 is operative through most or all ofthe remainder of the travel of lever 22, with the speed governor neverbecoming effective except in the event of a transient emergencycondition tending to produce a dangerous overspeed. At present, however,We prefer to use the manual control through shaft l5 during only a smallportion of the range of throttle movement, securing the principalcontrol through recalibration of the speed governor and using directcontrol through shaft 'I5 as a standby arrangement to become operativein the event the speed governor fails.

Our invention provides a fuel regulating system for aircraft gas turbinepowerplants including means for recalibrating the manual control so thata given setting corresponds to Ya iixed percentage of full rated loadregardless of altitude, and having speed and temperature responsivedevices arranged to enable operation at maximum safe load with economy,while at the same time preventing dangerously high speeds ortemperatures.

What we claim as new and desire to secure by Letters Patent of theUnited States, is:

l. In a regulating system for a thermal powerplant having a fuel controldev-ice for varying the fuel now in response to a variable pressuresignal, means for supplying control fluid at substantially constantpressure, a hydraulic motor with a first movable member biased by thepressure of control fluid in the motor in one direction, a'pilot valvefor regulating the flow of control iiuid from said means for supplyingto the motor, followup lever'means connecting the pilot valve to saidfirst movable member, means .for positioning the follow-up lever meansto vary the supply of control uid to the motor, adjustable resilientmeans biasing the first movable member in opposition to `the fluid.pressure in said motor, and servomotor means including a second movablemember in engaging relation with said `rst member and the adjustableresilient biasing means for modifying the action of said biasing meanson the first Vmovable member in response to a pressure appurtenant tothe operation of the powerplant, whereby the pressure supplied to thehydraulic motor is varied automatically regardless of the position ofthe follow-up lever.

2. ln a regulating system for a powerplant having a fuel control devicefor controlling fuel flow in response to a variable pressure signal, amain control lever adapted to -be positioned to select .a desired loadoutput, a hydraulic motor having a cylinder .and a piston slidablydisposed in the cylinder and forming a pressure chamber therewith, meansfor supplying a control fluid under pressure, pilot valve means forcontrolling the admission of control fluid to said chamber, follow-uplever means connecting the main con'- trol lever with said piston andthe pilot valve means, spring means, variable ratio lever meansconnected between .the spring and the piston to bias the piston againstfluid pressure in the cylin. der, and servo-motor means including amovable member connected to the variable ratio lever means for varyingthe biasing effect of the spring means yon said piston in response to apressure appurtenant to the operation of the powerplant, whereby thechamber pressure is automatically varied regardless of the position ofthe main control lever.

3. Ina powerplant control system having variable delivery fuel supplymeans, the combination of rst .duid pressure servo-motor means forvarying the `fuel delivery, second fluid pressure servo-motor meansproducing a signal pressure for positioning the rst servo-motor means,said second servo-motor means including means for supplying a controlfluid under pressure to a casing containing a first member movable inaccordance with the pressure of control iiuid supplied thereto, pilotvalve `means for regulating the admission or" .control iiuid from thesupply means lto .the second servo-motor means, conduit means`communieating the .pressure in the second servo-motor means to thefirst servo-motor means, .and follow-up lever .means connected .to thepilot valve .and .said nrst member, a control member engaging thefollow-up lever for positioning the pilot valve, adjustable meansbiasing said :movable member in the decrease fuel direction, andservo-motor means Aincluding a second movable member engaging theadjustable biasing .means for adjusting said biasing mea-ns in responseto a pressure appurtenant to the operation of the powerplant whereby thecontrol fluid pressure supplied to the first servo-motor means is variedautomatically in accordance with said operating `pressure of thepowerplant regardless of the position of said control member.

4. In la rotary thermal powerplant having `a hot gas generator and meansfor supplying fuel thereto at a variable rate, regulating means for thefuel supply including a movable member adapted to be positioned inaccordance with the fuel delivery desired, a control member connected tothe movable member for positioning the latter, means biasing the movablemember to one extreme of its range of movement, a governor `responsiveto 4a rotational speed condition in the powerplant and including amember adapted to move the control member in the decrease fuel directionwhen said speed rises above a predetermined value, a thermal deviceresponsive to a temperature Condition Vin the powerplant and including amember adapted to move the control member in the decrease fuel directionwhen said temperature condition rises to a preselected value, andservo-motor means responsive toa pressure varying as a function ofainbient atmospheric pressure for adjusting the force exerted on themovable member by said biasing means whereby the action of controlmember, speed governor, and thermal device are simultaneously modifiedin accordance with changes in said pressure.

5. lIn a fuel system .for a gas turbine powerplant having a hot gasgenerator and variable fuelsupply means including a uidpressure-responsive fuel control member -for adjusting the member,adjustable means biasing said movable member in the decrease fueldirection in opposition to said variable control pressure, means forpositioning said valve including a folloW-uplever connecting said valvewithl saidmovable member,

a control lever member engaging the follow-up' lever for positioning thevalve, means for adjusting the control lever to select a desired loadoutput, governor means responsive to a rotational speed condition in thepowerplant and adapted to movey the control lever in the decrease fuelVdirection irrespective of the position of the loadselecting means, athermal device responsive to a temperature condition appurtenant to theoperationv of the powerplant and also adapted to move the control leverin the decrease fuel direction independently of the position of the loadselecting means, and means responsive to a pressure conditionappurtenant to the operation of the powerplant for adjusting saidbiasing means to simultaneously modify the effect of the load selectingmeans, speed governor, and thermal device.

6. In a fuel control for a thermal powerplant, a hydraulic cylinder Witha slidable piston defining a pressure chamber, means for supplying acontrol fluid under pressure' tofsaid chamber, means for varying thefuel supply rate in accordance with changes of pressure in said chamber,a spring adapted to bias said piston against the pressure of the controlfluid, first means including a pilot valve connected to the piston by afollow-up lever for varying the pressure signal supplied to saidchamber, 'a variable ratio lever mechanism connecting the spring to thepiston, and means including a servo-motor connected to said mechanismand operable to vary the effective lever ratio in response to changes ina control pressure which is a function of ambient atmospheric pressure.

y7. In regulating mechanismA for a thermal powerplant, the combinationof a hydraulic cylinderA with a slidable piston defining a pressurechamber, means for supplying a control fluid under pressure to saidchamber, means for'varying the rate of fuel supply to the powerplant inaccordance with changes of pressure in said chamber, a spring adapted tobias said vpiston againstv the pressure of the control fluid, firstmeans including a pilot valve connected to said piston' by a follow-uplever for varying the pressure. signal supplied to said chamber,variable ratio mechanism connecting the spring to' the piston, and meansfor varying vthe ratio of said mechanism including a hydraulic vmotorwith a second pilot valve for regulating the flow of motive fluid to andfrom the motor, means responsive to a pressure varying as a function ofambient atmospheric pressure for positioning the second pilot valve, andmeans for limiting the rate of flow of motive uid in the decreasealtitude direction only whereby the regulating mechanism has a limitedrate of response with decreasing altitude While effecting rapid responsewith increasing altitude.

8. In a thermal powerplant having a hot gas generator'and means forsupplying fuel to the generator at a variable rate, a regulator for thefuel supply means including a control member, means for positioning thecontrol member to select a fuel rate corresponding to a `desired.output, a servo-mechanism including a thermal device re-- sponsive to atemperature condition appurtenant to the operation of the powerplant`and a hydraulic motor with an actuating member adapted to engage thecontrol member and move it in the decrease fuel direction, independentlyof the position of the output selecting means, means for supplyingmotive fluid under pressure, a pilot valve positioned by the thermaldevice and adapted to control the flow 'of fluid to and from thehydraulic motor, and means restricting the rate of flow of motivefluidto the motor in one direction only to limit the rate of response of theservo-motor with decreasing temperature While effecting rapid responsewith increasing temperature.

9. Regulating means for a thermal powerplant including a control member,means for positioning the controly member to select a desired heatrelease rate, a thermal servo-mechanism responsive to a temperaturecondition appurtenant to the operation of the powerplant and including ahydraulic motor with an actuating member adapted to engage the controlmember through a lost motion connection to move the latter in thedecrease output direction independently of the output selecting means,the degree of movement permitted by said lost-motion connection varyingwith the position of the control member and determining the temperaturerise which will occur before the servo-mechanism becomes effective todecrease the output, means for supplying motive uid under pressure, apilot valve positioned by the thermal device for controlling the flow offluid to and from the hydraulic motor,

and means restricting the rate of ow of motive' fluid in one directiononly to limit the rate of response of the servo-mechanism withdecreasing temperature While effecting rapid response with increasingtemperature.

-l0. In a control system for a rotary thermal powerplant having a heatgenerator and means for varying thefuel supply thereto including acontrol member the position of which determines the rate of fuel supply,the combination of'rst hydraulic motor means for positioning the fuelcontrol member, a second hydraulic motor vincluding a casing defining afluid pressure chamber and a member'movable in said chamber inaccordance with changes in the pressure therein, means for supplying acontrol'fluidunder pressure, pilot valve means for regulating the flowof control fluid from the supply means to said first and secondlhydraulic motors in parallel, follow-up lever means connecting thepilotvalve andA movable member of said second hydraulicA motor, acontrol lever member engaging the follow-up lever to position the pilotvalve first resilient means biasing the control lever in the increasefuel direction, means for positioning the control lever in the decreasefuel direction against the bias of said first resilient means to selecta desired load output, servo-mechanisms responsive to temperature andspeed conditions in the powerplant for moving the control lever in thedecrease fuel direction irrespective of the position of the loadselecting means, second biasing means connected to said movable memberthrough a variable ratio lever mechanism, and servo-motor means forvarying the effective moment arm of said variable lever in accordancewith a pressure condition'appurtenant to the operation of thepowerplant' whereby' the action ofthe load se'- lecting means and speedand`.temperature responsive means vare simultaneously modified inaccordance with changes in said applirtenant pressure.

`11. ,In a regulating system for a gas turbine powerplant navingmeansforvarying the output thereof, the Vcombination'. of a controllevermer'nberadapted to be 'positionedv in accordance with the outputdesired, means' for manual1y"position`V ing the control lever member tovselecta desired output, means responsive to a speed'appurten'ant tothe' operation of the 'powerplant'for actuating the `control lever in adirection to reduce the output regardless of the position of the outputselecting means in order to limit' said operating speed, toapreselected'value, means for adjusting said speed responsive device tovary said preselected value at which said device becomes' effective totake control away from the load selecting means,l and means'connectingsaidadjusting means with the" manual'cortrol means whereby while VtheSpeed responsive means isv vin voperative engage-` ment with"tlieycor'itrl levermember the output selecting' means remainsoutof'engagement with the control lever memberbut follows it with apredetermined clearance in position to quickly resume .control in theVevent of failure ofthers'peed responsive device.

12.'In a cnotrol system for a rotary, thermal powerplant for aircrafthaving a heat generator and'means for varying the fuel supply theretoincluding a control member the position of which determines the rate offuel supply, the combina,- tion lof rst hydraulic motor means forIpositioning the fuel control member, second hydraulic motorf meansincludingv s casing defining av Huid pressure chamber and a membermovable in said chamber in accordance with changes in the pressuretherein, means for supplying a control duid under pressure, 'pilot valvemeans for regulating the ow' ofcontrol duid from thesupplymeans to therst' and second hydraulic motors in parallel, follow-up lever meansVconnecting theA pilot valve and4 movable 4Irregiribfer hydraulic motor,a controllevermember engaging the'followup lever to 'position thepilot'valve, lirs't resilient means biasing the control lever injthein'creasing 'fuel direction, means for positioning the controlleverin the decrease Vfuel, direction against the bias of, said4 rstresilient meansv to select a desired loadV output, a first servomchanismrseensiveioa Speed condition in the iiowerrlat alrid having anactuating. memberv for moving the control 'lever through` aY lost;motion connection 'in the decreasefueldirection irrespective of theposition of theload selecting-means, the ydegree of lostlmotionpermitted by said connectionbeingproportional tothe speed risewhichwill. occur before' the servo-mechanism becomes,

effective to reduce the fuel supply, a second servomechanism responsiveto al temperature condi-. tion in the Ypo'werpla'nt and having; anactuating member adapted to lmove "the control lever throllgll a lostmotion connection in the decrease fuel. direction, the degree of motionpermitted by of said second 20 said connection being proportional to thetem; perature risewhich willv occur 'before the. second servo-mechanismbecomes eiective, the degreeof free movement in sai'd` lost'in'o'tionconnections varying asa vfunction of control lever position whereby "thespeed andl temperature rises permitted by the respective servos vary asa func--V tion of load setting, second "means biasing said movablemember 'through a vbrleiato'lver mechanism against" the Y*fluid pressurein said pressure chamber, and a third vcmnper'isatinglserv'o-mechanism`l for varying the` effective moment arm of vsaidvariable. lever in accordance with a' pressure condition which Varies asa tion of ambient atmospheric' pressure, wherebyV the actionof'th'e loadselecting means and speed and temperature servos are simultaneouslymodied in accordance with changesfin atmospheric pressure, said 'thermalservo-mechanism includ?, ing motor 'with'means limiting the rate ofmove-v ment ffe'cted thereby inbnedirection only to limit the 'rate of'response lthereof with" decreasing temperature while efecting'rapidresponse with increasingl temperature, said compens'atigservolmechanism' including a vx'n"ot'oi`wi`th` inea-ns for limiting"therate of"movement in one direction only whereby the rate 'of"'ies'por`1seJthereof is*vlimitedwith decreasing altitude While`e`re`ctin`afraDd'reSpOnSe Withincresihg altitude.

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